Method for removing incrustation from metal surfaces



United States Patent Oflice 3,544,366 Patented Dec. 1, 1970 3,544,366 METHOD FOR REMOVING INCRUSTATION FROM METAL SURFACES Carlo W. Uhlmann, Upper Merrion Square, Dublin 2, Ireland No Drawing. Filed Dec. 29, 1967, Ser. No. 694,396 Claims priority, application Ireland, Feb. 3, 1967,

Int. Cl. B0811 3/02; Clld 3/08 US. Cl. 134-2 6 Claims ABSTRACT OF THE DISCLOSURE A method for removing incrustation from metal surfaces by spraying a jet of an aqueous alkaline solution of the sodium salts of nitric and metasilicic acids, atomized by carbon dioxide under pressure, onto the metal surface which is heated to at least 80 C., silicic acid being formed when the jet meets the hot metal surface and thus causing the incrustation to assume a molten or vapour-like state.

This invention concerns an improved method for removing incrustation from metal surfaces, and means for carrying out the improved method. It concerns especially, but not exclusively, the surfaces which are exposed to the combustion products in boiler furnaces and the like. It also has application in cases where metal surfaces are incrusted with hard scale which it is difiicult or tedious to remove by known methods, as for example is frequently the case with metal castings.

Hitherto it has been the general practice to effect the removal of scale from the firebox walls and tubes in boilers and the like by first shutting off the burners, and after the boiler has cooled sufiiciently, to attack the scale with hammer, chisel and scraper, until all metal surfaces are clean. This is a slow and expensive procedure. It is entirely eliminated by the present invention which enables the scale to be removed in a relatively short time and without having to cool off the boiler.

The invention accordingly provides a method for removing incrustation from metal surfaces which comprises heating the metal to a temperature of at least 80 0, preparing an aqeeous alkaline solution of the sodium salts of nitric and metasilicic acids, atomizing, said solution with carbon dioxide under pressure and applying said atomized solution and carbon dioxide to the surface to be cleaned in the form of a jet, moving the point of application of the jet progressively over said surface, silicic acid being formed when the jet meets the hot metal surface thus causing the incrustation to assume a molten and vapour-like state. The alkaline solution is first prepared in a concentrated form by mixing 300 to 400 grams of sodium salts into 1 litre of water. The sodium salts are preferably comprised of from 15 to by weight, sodium nitrate, 45 to 55%, by weight, sodium metasilicate; the remainder may consist of other sodium salts such as, for example, trisodium phosphate. It is important, however, that the final solution should have a pH value of between 10 and 12. The .solution is pressurized with carbon dioxide which is under a pressure of between 10 and 15 atmospheres. The carbon dioxide also acts as a reaction agent in the formation of silicic acid which takes place when the atomized solution meets the hot metal surface.

In carrying out the cleaning operation the aqueous alkaline solution prepared as above described, which is diluted by adding about 9 to 10 times its weight of water, is placed in a metal container capable of safely withstanding pressure substantially higher than 15 atmospheres. The liquid advantageously occupies about fourfifths of the volume of the container. A capsule containing the carbon dioxide at a pressure of between 10 and 15 atmospheres is then screwed into the container and the latter is closed by a screw cap. The application of the cap serves to open the capsule so that the inside of the container together with the liquid therein is under high pressure. A flexible connection extends between the container and an atomizing nozzle mounted on one end of a metal tube of any appropriate length which may for example comprise a number of tubes joined together, and a manually operable control valve is located at the junction of the tube and the flexible connection referred to. The nozzle is of the type which can be swivelled in any direction and can be clamped in any selected position.

To operate the device it is only necessary for the operator to insert the nozzle-end of the tube into the firebox or the like to be cleaned by way of the fire door or other convenient aperture and to direct the nozzle to the metal surface to be cleaned, holding the nozzle only a few centimetres from the surface. On opening the control valve a finely atomized jet of the alkaline solution dispersed in carbon dioxide is powerfully applied on the incrusted surface to be cleaned, causing the incrustation to assume a molten and vapour-like state in which it may be taken up and removed with the hot gases passing to the flue, leaving the metal surfaces substantially clean as they are traversed by the jet.

It will be noted that in the case of a boiler furnace no preheating of the surface to be cleaned is required as the surface is already exposed to the hot furnace flames. The cleaning of the metal surfaces is most effective since the jets can penetrate into crevices and recesses where it would be diflicult to use mechanical scale removing scraping tools.

The following example illustrates one method of preparing an alkaline solution for use with the method of the invention.

EXAMPLE A mixture of sodium salts comprising 20% sodium nitrate 50% sodium metasilicate and 30% trisodium phosphate is prepared and 400 grams of the mixture is added to 1 litre of water. If desired, a small quantity of sodium hydroxide or other alkaline softening agent may be added so that the final solution has a pH value of between 10 and 12 and the sodium salts are prevented from crystallizing out of the solution. The solution is stored in suitable containers until such time as it is required for use whereupon it is substantially diluted as above described and placed in a metal container where it is placed under pressure by carbon dioxide at between 10 and 12 atmospheres.

The method of cleaning metal surfaces according to the invention is not confined to boiler furnace walls or tubes, but has a wide application for other purposes where dirt or the like require to be removed. For example, metal castings when delivered from the moulds often require to be pickled or sand-blasted in order to clean off adhering matter. Such surfaces, however, may be readily cleaned by the process according to the invention, being first heated to a suitable high temperature (e.g. C.) and then sprayed, preferably while applying a current of hot gas to carry off the dross as it is shifted from the surface under treatment.

What is claimed is:

1. A method for removing incrustation from metal surfaces which comprises heating the metal to a temperature of at least 80 C., atomizing an aqueous alkaline solution of the sodium salts of nitric and metasilicic acids with carbon dioxide under pressure, applying said atomized solution and carbon dioxide to the surface to be cleaned in the form of a jet, and moving the point of application of the jet progressively over said surface, silicic acid being formed when the jet meets the hot metal surface thus causing the incrustation to assume a molen and vapour-like state.

2. A method according to claim 1, wherein the carbon dioxide acts as an activating agent in the formation of the silicic acid and is under a pressure of between and atmospheres.

3. A method according to claim 1, wherein the alkaline solution consists of 300 to 400 grams of sodium salts to 10 litres of water.

4. A method according to claim 3, wherein the aqueous solution is first prepared as a concentrated solution using only 1 litre of water to 300 to 400 grams of sodium salts, subsequently diluted by the addition of approximately 9 litres of water.

5. A method according to claim 1, wherein the sodium salts are comprised of 15- to by weight, sodium nitrate, to by weight sodium metasilicate, the remainder also consisting of sodium-salts such that the pH value of the final solution is between 10 and 12.

6. A method according to claims, wherein trisodium phosphate is present in the proportion of 30%, by weight of the sodium nitrate and sodium metasilicate.

References Cited UNITED STATES PATENTS 2,439,784 4/1948 Cernd 1342X MORRIS O. WOLK, Primary Examiner SIDNEY MARANTZ, Assistant Examiner US. Cl. X.R. 

